The present invention relates generally to internal combustion engine ignition systems and more particularly to such a system of the contactless interrupt type.
Many present day ignition systems, including for example the conventional automobile ignition system, employ breaker points to interrupt the current flow in a spark coil primary thereby introducing a high spark-creating voltage in a secondary winding of that spark coil which is coupled either directly or by way of a distributor to a spark plug to provide the spark for igniting fuel to drive the engine. Such breaker points are susceptible to dirt, moisture, wear of the cam actuating arrangement, and point erosion due to arcing so as to require the point gap to be reset frequently and the contact points to be periodically replaced. Further, such systems employ a relatively large number of mechanical parts which are both costly and time consuming in original manufacture, as well as subsequent maintenance.
Numerous attempts have been made to eliminate the cam actuated breaker points and their attendant problems with these attempts generally being in the direction of providing all electronic ignition systems.
One frequently encountered type of electronic ignition system is the so-called capacitor discharge ignition wherein a charge is accumulated on a capacitor and then at the appropriate time electronic switching occurs to discharge the capacitor through the primary winding of a spark coil or high voltage transformer thereby providing the desired ignition spark from the transformer secondary winding.
Contactless interrupt type ignition systems represent another direction in which attempts at providing all electronic ignitions have progressed. Here, the current in the primary winding of a spark coil is interrupted as in the conventional breaker point type ignition, however, the interruption of that current flow is provided by an electronic switching arrangement. With this type system the storage capacitor with its potential for failure is eliminated, however, accurate timing and rapid interruption of the primary winding current flow have remained troublesome problems. Also in many of these systems the magnitude of the high voltage output is undesirably dependent upon engine speed.